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Discussion Starter #1
I keep hearing about how a false wall will add 6db to your midbass performance. How substantial does this wall need to be? Can I just quickly frame some drywall around my LCR's or does it need to be built out like a real wall?

Also, if I do this, I would like to have some room to play with toe in, can the openings be a bit bigger than the speaker so I can adjust toe in?
 

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Discussion Starter #5
Thanks.

That looks like way more than I want to tackle.

I was wondering is just having some rigid material between the speakers would work - like propping up peices if mdf or plywood but it sound like that wouldn't work
 

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What I don't like about it is that it's kinda permanent, meaning you can't play with placement. I'd rather have the option of moving things around.
 

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Discussion Starter #8
This is my problem. Also if you want to change speakers you have to start over unless they happen to be the same size.

I was hoping I could cut a price of plywood or mdf and just put them around my speakers without permanently building something.
 

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paul klipsch discussed this idea 40 years ago in the context of building some "false" corners for his corner loaded horns if they had to be place in a room where one or both of the front corners were not available.


i'll see if I can dig up the link. all you need to do is prevent the soundwave from travelling back around behind the speaker. that shouldn't require any sort of sturdy construction until the bass frequencies are large relative the room and are actually pressurizing it (in some sense).


not sure how to post the link.
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CB4QFjAA&url=http%3A%2F%2Fwww.computeraudiophile.com%2Fattachments%2Ff12-headphones-and-speakers%2F385d1336589653-sonus-faber-guarneri-memento-or-wilson-duette-dope-hope.pdf&ei=iOv8VO31GYGcgwSF44KQCA&usg=AFQjCNGGV8aycaDOvOwrmuzE1x88u7Lk4A


apparently he went pretty solid on his corners.


I think all that you would need is a board to keep the wave from coming back around it kind of like an open baffle speaker.


not sure if I'm losing my mind or if the spell checker is changing my words, but sometimes when I come back to see my post it has some strange grammatical errors that confuse the whole sentence. anyways...
 

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if the drivers are not mounted to the baffle then it doesn't have to be very sturdy.


a search on "google images" for open baffle speaker will give some examples of how sturdy it needs to be (which is not much at all).
 

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Discussion Starter #12
if the drivers are not mounted to the baffle then it doesn't have to be very sturdy.


a search on "google images" for open baffle speaker will give some examples of how sturdy it needs to be (which is not much at all).
Thanks! So my idea of framing around my speakers with some MDF or plywood may work. I cross these speakers at 80hz so they wouldn't be getting anything really low.
 

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it in a theoretical perfect baffle, it would increase the spl by the conjugate (opposite) of the amount of the baffle step compensation that was built into the speaker. who builds speakers that way anymore anyways? ;-)~
 

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baffle step follows the transition from 2pi to 4pi space.
this can be seen with this curve (which is a 24" sphere "baffle"):



from here: http://www.trueaudio.com/st_diff1.htm


the -3db down point (the half way point) can be calculated using this formula:







from: http://www.quarter-wave.com/General/BSC_Sizing.pdf


so in a typical room, it won't be the full 6db because real rooms aren't 4pi space beyond the baffle (the walls /ceiling/floor enclose some of the sound).


inputting 24" into the equation, gives a -3db point of 190hz, which matches up with the curve above.


so if you want to push the curve fall enough down to effectively have full loading of the driver in 2pi space at about 80hz, the baffle would probably have to have a midpoint of 40hz or even 20hz, which implies a baffle width of about 10-20 feet or effectively an entire baffle wall for a home environment.


now there is another possible option if you have front corners of the room open.


and that is to follow something like cowan did in his build.


http://www.cowanaudio.com/finale.html


that eliminates all the cancellations that normally create problems behind the speakers and give toe-in for good sound across the entire room.


 

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paul klipsch discussed this idea 40 years ago in the context of building some "false" corners for his corner loaded horns if they had to be placed in a room where one or both of the front corners were not available....

Those Klipsch newsletters are priceless!! Definitely a case of deja vu all over again...concepts covered include speaker toe in, phantom center channel vs a real center channel, making efficient speakers vs making space heaters (one of my favorites ! :eek: ). I just barely scanned the compendium.

Great stuff LTD !!

Mike
 
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